Description:
FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

“AN IMPROVED PROCESS FOR CHLORINATION OF METHYLPYRIDINES”
This patent application is an improvement over the invention filed in earlier Indian Patent Application No. IN201811010381, filed by the same applicant.

SRF LIMITED, AN INDIAN COMPANY,
SECTOR 45, BLOCK-C, UNICREST BUILDING,
GURGAON – 122003,
HARYANA (INDIA)

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to an improved process for producing trichloromethyl pyridines selectively by reacting methylpyridines with chlorine in an ionic liquid.

BACKGROUND OF THE INVENTION
Trichloromethyl pyridines are used as an intermediate for medicines, agricultural chemicals, and dyes especially herbicides.
Trichloromethyl pyridines can be prepared by rapidly mixing in the vapor phase, chlorine, an appropriate methylpyridine compound in an inert diluent and subjecting the mixture to temperatures of about 400-490°C or 240-270°C. The desired products can then be distilled from the resulting product stream.
U.S. Patent no. 3,412,095 discloses vapor phase chlorination of 4-picoline at a temperature in the range of 230-260ºC using steam as an inert medium and with a contact time of 3.8 seconds to give 4-trichloromethylpyridine.
Indian Patent Application No. 201811010381 filed by the same applicant discloses vapour phase chlorination of picolines to generate chlorinated trichloromethylpyridines. The vapour phase chlorination of methylpyridine initiates ring as well as side chain chlorination, resulting in mono and di-chlorinated trichloromethylpyridines, which are difficult to separate from the desired trichloropyridine.
It has been observed that methylpyridines can be selectively chlorinated in a good yield using chlorine in the presence of ionic liquids.
OBJECT OF THE INVENTION
The main object of the present invention is to provide simple, cost effective an industrially applicable and a selective process for preparation of trichloromethyl pyridines using chlorine in the presence of ionic liquids.

SUMMARY OF THE INVENTION
The present invention provides a process for preparation of trichloromethylpyridine, comprising the step of treating methylpyridine with chlorine in an ionic liquid.

DETAILED DESCRIPTION OF THE INVENTION
As used herein, the methylpyridine includes substituted or unsubstituted methylpyridines selected from a group consisting of 2-methylpyridine; 3-methylpyridine and 4-methylpyridine or the like.
As used herein, the trichloromethylpyridines, includes substituted or unsubstituted trichloromethylpyridines selected from a group consisting of 2-trichloromethylpyridine; 3-trichloromethylpyridine and 4-trichloromethylpyridine or the like.
In an embodiment, the present invention provides a process for preparation of trichloromethylpyridine, comprising the step of treating a methylpyridine with chlorine in an ionic liquid at a temperature in the range of 60 to 180oC.
In another embodiment, the present invention provides a process for preparation of trichloromethylpyridine, comprising the step of treating a methylpyridine with chlorine in an ionic liquid at a temperature in the range of 120 to 160oC.
In an embodiment of the present invention, chlorine is used in the range of 3 to 10 mole equivalent with respect to the methylpyridine.
In an embodiment, the present invention provides a process for preparation of trichloromethylpyridine, comprising the step of treating methylpyridine with chlorine in an ionic liquid selected from a group consisting of imidazolium chloride, 1-decyl-3-methylimidazolium chloride, piperidinium chloride, pyrrolidinium chloride, pyridinium chloride, morpholinium chloride, ammonium chloride, phosphonium chloride, sulphonium chloride, 1-butyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-(2-hydroxyethyl)-3- methylimidazolium chloride, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-3-propylimidazolium chloride, 1-benzyl-3-methylimidazolium chloride, 1-methyl-1-propylpiperidinium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butylpyridinium chloride, 1-butyl-4-methylpyridinium chloride, 1-ethylpyridinium chloride, 1-propylpyridinium chloride, 4-ethyl-4-methylmorpholin-4-ium chloride, trihexyl(tetradecyl)-phosphonium chloride and tetrabutylammonium chloride or the like.
In another embodiment, the process of present invention is carried out in absence of a solvent.
In another embodiment, the process of present invention is carried out in a non-polar solvent selected from a group consisting of halogenated aliphatic and aromatic solvent such as bromodichloromethane, dibromochloromethane, trichlorofluoromethane, dichloromethane, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, cis-1,2-dichloroethylene, trans-1,2-dichloroethylene, trichloroethylene, tetrachloroethylene, 1,2-dichloropropane, trans-1,3-dichloropropylene, bis(chloro)methyl ether, bis(2-chloroethyl)ether, bis(2-chloroisopropyl)ether, 2-chloroethylvinyl ether, chlorobenzene, o-chlorobenzene, m-chlorobenzene, trichloroacetonitrile, chloroform, carbon tetrachloride, trichloroethane, 1,1,1,2-tetrachloroethane and 1,1,2,2-tetrachloroethane or the like.
In another embodiment, the process of present invention selectively provides trichloromethylpyridine of purity 98-99.9%.
In another embodiment, the process of present invention selectively provides trichloromethylpyridines, substantially free of ring chlorinated impurities.
As used herein, the term substantially free of ring chlorinated impurities refers to less than 1% of ring chlorinated impurities, preferably ring chlorinated impurities in the range of 0.001-1%.
As used herein, the ring chlorinated impurities, includes chlorinated trichloromethylpyridines selected from a group consisting of 3-chloro-2-trichloromethylpyridine; 4-chloro-2-trichloromethylpyridine; 5-chloro-2-trichloromethylpyridine; 6-chloro-2-trichloromethylpyridine; 2-chloro-3-trichloromethylpyridine; 4-chloro-3-trichloromethylpyridine; 5-chloro-3-trichloromethylpyridine; 6-chloro-3-trichloromethylpyridine; 2-chloro-4-trichloromethylpyridine; 3-chloro-4-trichloromethylpyridine; 6-chloro-4-trichloromethylpyridine; 4,6-dichloro-2-trichloromethylpyridine; 2,6-dichloro-3-trichloromethylpyridine; 2,6-dichloro-4-trichloromethylpyridine; 4-chloromethlpyridie and 4-dichloromethyl pyridine or the like.
The trichloromethylpyridines may be isolated by using techniques known in the art for example distillation, extraction, evaporation, column chromatography and layer separation or combination thereof.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The completion of the reaction can be monitored by any one of chromatographic techniques such as thin layer chromatography (TLC), high pressure liquid chromatography (HPLC), ultra-pressure liquid chromatography (UPLC), Gas chromatography (GC) and alike.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLES
Example 1: Process for preparing 2-trichloromethylpyridine
1-Decyl-3-methylimidazolium chloride (16.5 g, 63.7 mmol) was added to 2-picoline (10.7 g, 83 mmol; in form of hydrochloride salt) and the reaction mass was heated gradually to 145°C. Chlorine gas was purged to the above reaction mixture at 145-150°C and the reaction was monitored by GC. After completion of reaction, the reaction mass was cooled and diluted with dichloromethane (50 g). The above diluted reaction mass was neutralized with sodium carbonate solution (10%, 80 g). The organic layer was separated, concentrated, and distilled to obtain the titled product.
Analysis: Yield: 72%; Purity (by GC): 98.5%; chlorinated 2-trichloromethylpyridine: 0.01%
Example 2: Process for preparing 3-trichloromethylpyridine
The process of Example 1 was repeated by using 3-picoline HCl as reactant to obtain the following results:
Analysis: Yield: 75%; Purity (by GC): 99.1%; chlorinated 3-trichloromethylpyridine: 0.01%

Example 3: Process for preparing 4-trichloromethylpyridine
The process of Example 1 was repeated by using 4-picoline HCl as reactant to obtain the following results:
Analysis: Yield: 72%; Purity (by GC): 98.5%; chlorinated 4-trichloromethylpyridine: 0.02%
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention and specific examples provided herein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention that come within the scope of any claims and their equivalents.

, C , Claims:WE CLAIM:
1. A process for preparation of trichloromethylpyridine, comprising the step of treating methylpyridine with chlorine in an ionic liquid.
2. The process as claimed in claim 1, wherein methylpyridine is treated with chlorine at a temperature in the range of 60-180°C.
3. The process as claimed in claim 1, wherein chlorine is used in the range of 3 to 10 mole equivalent with respect to the methylpyridine.
4. The process as claimed in claim 1, wherein the ionic liquid is selected from a group consisting of imidazolium chloride, 1-decyl-3-methylimidazolium chloride, piperidinium chloride, pyrrolidinium chloride, pyridinium chloride, morpholinium chloride, ammonium chloride, phosphonium chloride, sulphonium chloride, 1-butyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-(2-hydroxyethyl)-3-methylimidazolium chloride, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-3-propylimidazolium chloride, 1-benzyl-3-methylimidazolium chloride, 1-methyl-1-propylpiperidinium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butylpyridinium chloride, 1-butyl-4-methylpyridinium chloride, 1-ethylpyridinium chloride, 1-propylpyridinium chloride, 4-ethyl-4-methylmorpholin-4-ium chloride, trihexyl(tetradecyl)-phosphonium chloride and tetrabutylammonium chloride.

5. The process as claimed in claim 1, wherein the process provides trichloromethylpyridine of purity 98-99.9%, having ring chlorinated impurities in the range of 0.01-1%.

Dated this 31st day of October 2022.

WE CLAIM:
1. A process for preparation of trichloromethylpyridine, comprising the step of treating methylpyridine with chlorine in an ionic liquid.
2. The process as claimed in claim 1, wherein methylpyridine is treated with chlorine at a temperature in the range of 60-180°C.
3. The process as claimed in claim 1, wherein chlorine is used in the range of 3 to 10 mole equivalent with respect to the methylpyridine.
4. The process as claimed in claim 1, wherein the ionic liquid is selected from a group consisting of imidazolium chloride, 1-decyl-3-methylimidazolium chloride, piperidinium chloride, pyrrolidinium chloride, pyridinium chloride, morpholinium chloride, ammonium chloride, phosphonium chloride, sulphonium chloride, 1-butyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium chloride, 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride, 1-(2-hydroxyethyl)-3-methylimidazolium chloride, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-3-propylimidazolium chloride, 1-benzyl-3-methylimidazolium chloride, 1-methyl-1-propylpiperidinium chloride, 1-butyl-1-methylpyrrolidinium chloride, 1-butylpyridinium chloride, 1-butyl-4-methylpyridinium chloride, 1-ethylpyridinium chloride, 1-propylpyridinium chloride, 4-ethyl-4-methylmorpholin-4-ium chloride, trihexyl(tetradecyl)-phosphonium chloride and tetrabutylammonium chloride.

5. The process as claimed in claim 1, wherein the process provides trichloromethylpyridine of purity 98-99.9%, having ring chlorinated impurities in the range of 0.01-1%.

Dated this 31st day of October 2022.